1. Field of the Invention
The invention is directed generally to marine engine drive systems designed to supply rotary power down from an engine carried on a boat to a submerged propeller and for imparting the propelling force generated by the rotating propeller in the water back to the boat thereby causing the boat to travel across the water. More particularly, the invention relates to a single hydraulic trim cylinder configuration for pivoting the drive system across a range of possible trim and tilt positions.
2. Background
Traditionally, powerboats have been powered with either an inboard engine, an outboard engine, or an inboard/outboard engine. In the inboard configuration, the engine is typically positioned within an engine compartment or engine room that is carried on the boat. A drive shaft of the assembly extends through a bottom surface of the hull of the boat with a propeller positioned thereupon, but exteriorly to the boat. The drive shaft and propeller remain in the water during normal operation of the boat and typically cannot be removed from the water unless the boat is also taken out of the water. Often, an inboard engine is completely concealed within the engine compartment or engine room below the deck of the boat.
An outboard engine is a self contained unit that is most often attached to the transom of a boat. A typical outboard engine configuration includes an engine that is completely concealed within a cowling, at least one propeller attached to a lower unit, and a drive shaft contained within a drive shaft housing that extends in a generally vertical direction between the engine and the lower unit. The lower unit is typically constructed as a one piece body that is made of aluminum. Further, the lower unit contains gears for transferring torque produced by the engine, and imparted on the drive shaft, to a propeller shaft that is generally oriented perpendicularly to the drive shaft. The lower unit includes a skeg for steering purposes, an anti-cavitation plate, and a cylindrical bore that houses a forward gear, a reverse gear, and a propeller shaft. The lower unit usually also includes water intake ports for receiving raw water that is used to cool the engine. Further, the lower unit is coupled to a drive shaft housing, or upper housing, using a set of five to ten bolts.
Most outboard engines manufactured today further include a tilt/trim system that enables the outboard engine to be tilted through various angles to improve the performance of a boat and to rotate the lower end of the power plant out of the water. Generally, outboard engines can be trimmed between angles relative to a vertical axis of about minus 5 degrees to about plus 15 degrees and can be tilted through a range of angles between 15 degrees and about 60 degrees. The trim/tilt system generally is composed of three hydraulic cylinders, one cylinder that is the tilt mechanism and two cylinders that combine with the tilt cylinder to form a trim mechanism. The trim range includes a range of angles within which an engine can be operated to power the carrying boat while a tilt range includes a range of angles within which the engine generally will not be operated to power the boat; that is, the tilt range is for use when the engine is not running. The trim function moves the engine through the described range of angles about half as fast as the tilt function moves the engine because trim adjustment is used to adjust the drive leg through the trim range of angles when the boat is traveling, often at relatively high rates of speeds. Further, the trim feature operates at this reduced speed for safety concerns since relatively small trim adjustments can significantly affect the attitude of the boat. It also permits an operator to fine tune the travel position of the boat as it travels across the water for enhanced performance.
The tilt mechanism typically enables an entire outboard engine, or substantially all of the engine, to be tilted out of the water while the boat remains in the water. This feature is advantageous for many reasons. It is used during the boat launch and the retrieval process to protect the drive unit, and particularly the lower end from damaging strikes. Even if the boat is not removed from the water, the positioning of the drive leg outside the water using the tilt function prevents aquatic growth, such as algae, barnacles, and other marine plants and animals, from developing on the lower unit. Water, and especially salt water, can be highly corrosive. Salt water corrodes metals and provides a prime environment for galvanic reactions that accelerate decay of metals. Thus, removing the drive assembly from the water when not in use can increase its life dramatically.
The inboard/outboard engine configuration is a hybrid between the inboard and the outboard engine configuration just as the name implies. The inboard/outboard engine configuration generally includes a motor that is positioned within an engine compartment, much like the inboard engine configuration. Unlike the inboard engine which may be located mid-ship, however, the inboard/outboard engine compartment is typically located proximate the transom of the boat. The inboard/outboard engine further includes a drive assembly resembling the lower unit of an outboard engine. The drive assembly of an inboard/outboard power plant, however, is not coupled to a drive housing as described above relative to outboard engines. Instead, the drive assembly includes a shield assembly that is coupled to the transom of a boat.
The drive assembly of the inboard/outboard engine further includes a tilt/trim assembly that has a function similar to the tilt/trim assemblies found on outboard engines and described above. The conventional tilt/trim assemblies for inboard/outboard engines, however, are usually designed differently than those for outboard engines. Specifically, the conventional inboard/outboard tilt/trim assemblies include two hydraulic cylinders. One hydraulic cylinder is attached to one side of the drive assembly proximate the cavitation plate and the other hydraulic cylinder is attached to the other side of the assembly near the cavitation plate. Each cylinder is oriented generally parallel to the cavitation plate. With the hydraulic trim cylinders attached in this fashion, the cylinders produce unwanted water spray during operation of the engine while the boat is traveling on plane. Specifically, as the boat is planing, water travels on top of the cavitation plate and contacts the hydraulic cylinders near where they are attached to the drive assembly. The water is deflected and forms a spray that is unattractive and can cause the back portion of a boat to become wet, including any nearby passengers.
Though there are some drawbacks to traditional inboard/outboard designs, the design still possesses attributes that make it highly desired by many boaters. For instance, inboard/outboard engines can include a closed-loop water cooling system that uses recirculated cooling fluid. This closed-loop system eliminates corrosion problems associated with using raw salt water as encountered in outboard engine. Because a closed-loop cooling system weighs significantly more than a raw water cooling system, typical outboard motors do not have closed-loop water cooling systems. Further, the inboard/outboard engine is usually quieter than most outboard engines and thus desired by some boaters. Additionally, the low profile of inboard/outboard power plants do not provide an obstacle at the transom of the boat, such as the obstacle produced by the elevated engine portion of an outboard power plant. Instead, a relatively unobstructed transom is presented by the low-rise inboard/outboard power plant. As a result, inboard/outboard engines allow boats to include unobstructed swim platforms that extend across the entire transom of a boat which is something that is not normally possible when using an outboard engine. Thus, these and other attributes not mentioned make an inboard/outboard engine the desired engine for many boating applications.
As indicated above, the inboard/outboard engine has a number of disadvantages. In contrast to the outboard engine and the inboard engine, the inboard/outboard engine exposes more parts to the harsh environment of salt water. As mentioned above, the outboard engine is self-contained and is capable of being tilted completely out of the water using the trim mechanism. Further, the inboard engine has only a drive shaft and a propeller that are exposed to the water. The inboard/outboard, on the other hand, cannot usually be rotated completely out of the water when the boat is floating. Thus, anytime the boat remains in the water, the drive assembly at least partly remains in the water. Still further, the inboard/outboard engine has additional parts, such as the shield assembly, exhaust tubes, oil hoses, shift rods, covering sheaths, and a gimbal ring, that are exposed to the water, and are thus also subject to corrosion. As a result, these additional parts that are exposed to the water increase the need for service and increase the potential for breakage.
As described above, both outboard engines and inboard/outboard engines have lower units that transfer torque from a generally vertical drive shaft to a propeller drive shaft that is generally perpendicular to the vertical drive shaft. The lower unit typically contains a skeg, a lower chamber capable of receiving gears, bearings and the propeller drive shaft, one or more raw water intake ports that are connected to a raw water chamber and conduit system, and an anti-cavitation plate. Generally, the lower unit is a unitary member that is constructed of aluminum and formed by die-casting. The lower unit is composed of aluminum to withstand heavy blows caused by hitting submerged objects, such as logs, pilings and other debris, and from running aground. Further, the lower unit has been constructed of aluminum to handle the forces generated by the moment arm produced by the propulsion unit, most typically in the form of a rotating propeller, acting at the bottom of the lower unit. It is the lower unit coupled with either a drive housing or a shield assembly that provides the structural integrity of a typical drive system. Additionally, the lower unit is desirably designed to present an exterior surface that allows the drive system to move through water with a minimized hydrodynamic drag.
In addition to providing a hydrodynamically efficient exterior shape, lower units of traditional stern drives have included raw water intake ports and conduits, and exhaust conduits. The common designs for the raw water and exhaust conduits have been inefficient and susceptible to corrosion. More specifically, the conduits are inefficient flow conveyances because their configuration has previously been dictated by the die-cast manufacturing processes for these substantially solid, or thick-walled bodies. That is, the conduits or channels were conventionally formed between the outside surfaces of the exterior walls of the lower unit and the interior walls that formed the central cavity provided to receive a drive shaft therein. In other words, traditional service conduits have been formed in the wall""s thickness of the lower unit. Still further, the conduits are often formed as right angle channels, or near right angle channels and resultingly include corner spaces at these right angle turns where eddies form and other flow restricting phenomena occur. Additionally, when the drive assembly is used in salt water, these areas are prone to collecting salt which accelerates corrosion. While this problem is well known, simply adding more material to eliminate these places of poor flow is not the answer because this simply adds more weight to an already over weight machine.
The bifurcated upper unit/lower unit design is problematic in its own right. For instance, the joint between the two units requires a seal that frequently corrodes and leaks. Further, while the lower unit has a raw water unit conduit that is formed from the inside surface of the exterior walls, the raw water conduit located within the upper unit is typically composed of a tubing or pipe. As a result, some structure for connecting the raw water conduit of the lower unit to the raw water conduit of the upper unit must be included. As with all fluid connections, each detrimentally presents a heightened potential for leakage.
Thus, a need exists for a drive assembly for an inboard/outboard or an outboard engine that resists corrosion while maintaining or improving the strength and hydrodynamic qualities found in conventional drive systems. Further, a need exists for an inboard/outboard engine having a tilt/trim mechanism that does not result in unwanted water spray. As always, there is a constant desire for less complex drive assemblies that are more efficient to manufacture and assemble, and are ultimately more reliable because of their simplicity. Finally, a need exists for an improved cooling and exhaust system for marine engines.
Set forth below are summaries of primary aspects of systems and methods configured and practiced according to the presently disclosed inventions. These features address one or more of the foregoing problems, and/or provide further benefits and advantages as will become evident from the included descriptions.
In at least one embodiment, one aspect of the presently disclosed inventions takes the form of a stern drive assembly that is configured for utilization in an inboard/outboard power plant for a boat. The stern drive assembly includes a central rigid core that is configured at an upper portion to be coupled to the stern of a carrying boat. A lower portion of the core is designed to accept a boat-moving force generated by a water propulsion unit that is coupled thereto. The term coupled shall be taken to mean a connection, but not necessarily a direct connection. That is, certain other components may be interstitially located, or connected between, those components that are specified as being coupled, or couplable, together. Water propulsion units take various forms; among others, single and dual rotating propellers are included, as well as marine jet propulsion systems. A thin-walled housing is configured to be secured about a predominance of the centrally located rigid core. In this context, the term predominance should be taken to mean greater than one-half or fifty percent. The housing has an outer surface that establishes an exterior of the stern drive assembly and an inner surface directed generally toward the central rigid core. A portion of an exterior surface of the central rigid core is configured to cooperate with a corresponding portion of the inner surface of the thin-walled housing. These two portions, when in cooperative orientation one with the other, form a functional feature for the stern drive assembly.
One example of such a functional feature is a fluid flow passage that is configured to carry fluids through the stern drive assembly during operation. A special characteristic of at least some of these flow passages is that a part of the passage curvaceously shaped for facilitating fluid flow therethrough. When the walls of such fluid flow passages are curved, as opposed to having sharp turns and corners, the resistance to movement of fluids passing therein is minimized. As specific examples, an individual fluid flow passage may exemplarily be configured as an exhaust channel or a coolant water channel, typically conveying fluids, both gases and liquids, to and/or from the powering engine of the boat.
The thin-walled housing is generally spaced apart from the central rigid core. In this way, a working space is formed between the two components. Preferably, the working space is provided to accommodate location of the functional feature(s), such as an exhaust channel, therein. In at least one example, the working space is maintained by one or more spacing ribs that are abuttingly positioned between the thin-walled housing and the central rigid core. Among the several spacing ribs, at least two are transversely oriented to at least one of the others. That is to say, these two exemplary ribs are not parallel to each other, but are instead positioned at some angle to one another. The angle need not necessarily measure ninety degrees, but does measure some other than zero degrees so that the thin-walled housing is fortified against flexure by the rib""s inclusion. This transverse orientation of the ribs is often a natural consequence of their configuration to form a required functional feature. With respect to the thin-walled housing, the ribs are preferably oriented at approximate right angles to the housing""s inner surface.
In a like manner, such functional features can be formed, at least partially, by similarly configured ribs that extend from the central rigid core. In one particularly preferred embodiment, the functional feature, such as an exhaust channel, is formed through a cooperation of ribs that extend from the thin-walled housing and ribs that extend from the central rigid core.
In a preferred construction, the thin-walled housing is formed from at least two clam-shell style cowlings that are configured for mating engagement along perimeter portions of the shells. An advantageous material of construction is impact resistant, resin and fiber based composite. To promote structural integrity of the housing, the two clam-shell style cowlings are cemented together, and as a unit, form the exterior presentation of the stern drive assembly. Further support is provided to the housing when it is cemented to the central rigid core for substantially permanent fixation together.
In order to affect sufficient structural fortitude while maintaining a necessary degree of flexure, an average composite thickness ranging from about 2 mm to about 10 mm is preferred. In practice, an average composite thickness of about 3 mm has been found to strike an advantageous balance between the desired performance characteristics of durability which requires a certain degree of ductility, and rigidity which is needed for efficient force transmission.
To enhance the performance of the stern drive assembly, the central rigid core is unitarily constructed, preferably from aluminum, thereby forming a monolithic member that extends between the upper and lower portions of the core.
According to another aspect, this invention is directed to a drive assembly for propelling a boat through water by coupling an engine to at least one propeller. This drive assembly replaces the conventional lower unit and its support structure that have traditionally been used in outboard and inboard/outboard power plants. Specifically, the drive assembly can include, in part, a drive frame extending aft from a transom of a boat with a first cowling covering substantially all of a first side of the drive structure and a second cowling covering substantially all of another side of the drive frame opposite the first side. The cowlings provide, in part, a hydrodynamically efficient exterior shape for the drive frame. The drive frame can include an upper chamber, a middle chamber, and a lower chamber. The upper chamber is sized to receive a clutch assembly having a plurality of gears for transferring rotational motion from a generally horizontal drive shaft coupled to an engine to a generally vertical drive shaft. The middle chamber receives the generally vertical drive shaft, and the lower chamber receives a combination of gears, bearings and a propeller shaft.
The exterior surface of the drive frame may include one or more ribs for attaching the cowlings to the drive frame and for supporting the cowlings. The internal surface of the cowlings can contain laterally extending members configured to mate with the ribs of the drive frame to provide a surface for attaching the cowlings to the drive frame and for supporting the cowlings. Additionally, the perimeter of the cowlings contain a cowling connection system that can exemplarily take the form of a tongue and groove system. For instance, one cowling can have a tongue positioned on the inner surface of its perimeter and the other cowling can have a groove capable of receiving the tongue that is positioned on its inner surface. Alternatively, the cowling connection system can include other connection devices discussed below.
The cowlings establish the outside surfaces of the drive frame and provide the drive frame with a more efficient hydrodynamic exterior surface. Additionally, the cowlings have semi-conduits formed on their internal surfaces that when mated with semi-conduits formed on the exterior surfaces of the drive frame, form completed conduits. These conduits are used, for example, to transport cooling water from the water intake ports located in the cowlings to an engine cooling system. Additionally, such conduits may be used to transport exhaust gases and cooling water from the engine through a plurality of exhaust ports.
In one embodiment, the cowlings can be formed from a composite material. Tests have proven resin and fiber based composite material to be extremely durable and capable of performing exceptionally well in this application. A drive assembly constructed with cowlings manufactured from this material is about 40 pounds lighter than a comparable conventionally designed drive assembly, which correlates to about a 20 percent decrease in weight. Alternatively, the cowlings can be formed from other suitable materials.
The drive system can be assembled using an adhesive, such as an epoxy, that is placed along the perimeter of the cowlings and on the laterally extending members that mate with the ribs. Preferably, the adhesive forms a permanent bond so that once the cowlings are attached to the drive frame and to each other, they cannot be separated. Thus, the cowlings and the drive frame form a monolithic structure. Alternatively, the cowlings can be attached to the drive frame using mechanical connectors such as screws, nuts and bolts.
The drive frame is pivotably coupled to a gimbal ring, thereby enabling the drive frame to rotate about a generally horizontal axis so that the trim and tilt position of the drive assembly can be adjusted. Further, the gimbal ring is pivotably mounted to a shield assembly that allows the gimbal ring, together with the drive frame and attached cowlings, to rotate about a generally vertical axis for steering purposes. In addition, a single trim cylinder is coupled to the drive frame at one end and to the gimbal ring at the other end. Importantly, the single trim cylinder attaches to the drive frame on the side of the drive frame facing the transom of the boat. In this configuration, the single trim cylinder does not come in contact with the moving water as the carrying boat is on plane. Therefore, no water spray is caused by the single trim cylinder.
An advantage of such a drive system is that the system allows for the exterior surface of the drive system to be composed of a non-metallic material. As a result, less metal surface area is exposed to salt water and, thus, there is less corrosion.
Yet another advantage of the new drive system is that it contains thirty percent fewer parts than a comparable conventionally designed drive assembly. This fact is due, at least in part, to the use of an adhesive to couple the assembly together rather than bolts, as used in conventional drive systems. There is also the elimination of the interface between an upper and lower unit. The formation of fluid channels such as raw water conduits and exhaust conduits on the external surface of the drive frame and the internal surfaces of the cowlings is also new.
Another advantage of this system is that the drive frame provides the necessary support for the forces generated by the propeller. While the cowlings provide some support to the drive frame, the majority of the structural support is provided by the drive frame. As a result, the cowlings can be designed without taking this type of structural support into account. Instead, the cowlings are designed to a specification for withstanding leading-edge impacts such as that suffered when an object floating in the water is struck by the submerged portion of the power unit as it slices through the water. Other design features of the cowlings include a minimization of hydrodynamic drag and flow resistance to cooling water and exhaust passing through conveyances for such fluids in the drive assembly. These several features are provided by the invention, all while enclosing and protecting the working parts of the drive assembly.
Yet another advantage of this system is that the raw water conduit formed by the cowlings increases water circulation through an engine water cooling system by about fifty percent.
Still another advantage of this system is that the exhaust conduit formed by the drive frame and the cowlings reduces the back pressure that is typically found in engine systems using conventional drive systems.
Another advantage of this system is that the raw water conduit and the exhaust conduit do not include spaces where eddies can form and salt can accumulate.
Still another advantage of this system is that the exterior shape of the cowlings results in ten percent less hydrodynamic drag than conventional drive assemblies. Further, the cowling generates vertical lifting forces that are translated to the drive assembly and to the boat, thereby enhancing the performance of the boat.
Another advantage of this invention is that the drive assembly includes a single hydraulic trim cylinder for trimming and tilting the engine. This reduces a manufacturer""s warranty costs significantly and reduces the number of parts susceptible to failure.
Yet another advantage of this system is that the single hydraulic trim cylinder is coupled to the drive assembly so that it is not in contact with the moving water while the carrying boat is on plane. Therefore, the single hydraulic trim cylinder does not produce undesirable water spray that is typical of hydraulic trim cylinders used with convention inboard/outboard drive cylinders.
These and additional advantages will become evident to those skilled in the art from the drawings and detailed description that is provided herewith.